Support contact discovery

[nanu-c]

This currently not possible and it looks like, it takes a lot of effort. I did some experiments but there is a lot todo.

[rubdos]

There's also two sides to this, correct? Registration with PNI instead of plain phone number (which will, I assume, soon be mandatory), keeping that registration current, and then the lookup part.

Do you have some documentation on what needs to happen?

[nanu-c]

I am not sure, with "we need the pni". Actually it works now similar to the group directory.

• Ask "/v2/directory/auth" for a cdsi credential
• Optional: use the token from the previous contact discovery request
• do parseAndSortE164Strings
• use the cdsi credential to make an request
• parse the result and update the contacts storage

The logic is still implemented in Java for signal android
https://github.com/signalapp/Signal-Android/blob/63cca2de6668c11e20c4c506fd61513d42c49711/app/src/main/java/org/thoughtcrime/securesms/contacts/sync/ContactDiscoveryRefreshV2.kt#L131

https://github.com/signalapp/Signal-Android/blob/90695182f34a747058ca6bc3c86156fe51f24885/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java#L487